面向对象-继承与多态

星哥玩云

发布于 2022-09-08 13:14:15

3780

发布于 2022-09-08 13:14:15

文章被收录于专栏：开源部署

一、继承的概念

二、单继承的实现

人类（person.py）

class Person(object):
    def __init__(self, name, age, sex, money):
        self.name = name
        self.age = age
        self.sex = sex

        #私有属性
        self.__money = money

    @property
    def money(self):
        return self.__money
    @money.setter
    def money(self, value):
        self.__money = value

    def run(self):
        print("---------run")

学生类（student.py）

from person import Person

class Student(Person):
    def __init__(self, name, age, sex, money, stuId):
        # 调用父类中的__init__函数
        super().__init__(name, age, sex, money)
        # 增加独有属性
        self.stuId = stuId
    # 增加独有的方法
    def say(self):
        print("---------say")
    # 重写run方法
    def run(self):
        print("student run")
        super().run()#执行父类中的方法(原功能)

工人类（worker.py）

from person import Person

class Worker(Person):
    def __init__(self, name, age, sex, money, gl):
        super().__init__(name, age, sex, money)
        self.gl = gl
    def talk(self):
        print("---------talk")

主文件（main.py）

from student import Student
from worker import Worker

def main():
    stu1 = Student("dily", 30, "男", 100, 1)
    wor1 = Worker("wangbw", 40, "男", 200, 20)

    # 方法的使用原理：当对象调用方法时，首先现在本类中查找同名方法，找到了就用，找不到去直接父类中查找，父类中有就用，没有的话再去上一级父类中查找，直到找到object中截止，在哪里找到就用哪里方法。如果没有没有找到那么就报错说明没有该方法
    stu1.run()
    wor1.run()

    stu1.say()
    wor1.talk()

    # 私有属性可以被继承
    print("---------", stu1.money)

if __name__ == "__main__":
    main()

三、重写

目的：将继承的方法重写一遍，在原有的功能基础上可以添加一些新的功能

class Person(object):
    # 重写：将继承的方法重写一遍，在原有的功能基础上可以添加一些新的功能
    def __init__(self, name, age):
        self.name = name
        self.age = age

    # 在用户调用print打印该类型的对象时
    # 显示给用户的
    def __str__(self):
        return "1-name:%s,age:%d"%(self.name, self.age)

    # 是给机器用的，在python解释器里直接敲对象时被调用
    def __repr__(self):
        return "2-name:%s,age:%d" % (self.name, self.age)
per = Person("liudh", 55)
print(per)
# print(per.name, per.age)

四、多继承的实现

加法类（add.py）

class Add(object):
    def __init__(self, m, n, a):
        self.m = m
        self.n = n
        self.a = a
    def sum(self, x, y):
        return x + y
    def say(self):
        print("sunck is a good man")

减法类（sub.py）

class Sub(object):
    def __init__(self, m, n, b):
        self.m = m
        self.n = n
        self.b = b
    def sub(self, x, y):
        return x - y
    def say(self):
        print("sunck is a nice man")

计算器类（calculate.py）

from add import Add
from sub import Sub

# 多继承：在小括号中依次写入父类
class Calculate(Add, Sub):
    def __init__(self, m, n, a, b):
        Add.__init__(self, m, n ,a)
        Sub.__init__(self, m, n ,b)

主文件（main.py）

from calculate import Calculate

def main():
    c = Calculate(1,2,3,4)
    print(c.m)
    print(c.n)
    print(c.a)
    print(c.b)

    #父类中的方法名相同，默认调用的是括号中排名靠前的父类中的方法
    c.say()

if __name__ == "__main__":
    main()

五、Mixin

概念

Mixin编程是一种开发模式，是一种将多个类中的功能单元的进行组合的利用的方式，这听起来就像是有类的继承机制就可以实现，然而这与传统的类继承有所不同。通常mixin并不作为任何类的基类，也不关心与什么类一起使用，而是在运行时动态的同其他零散的类一起组合使用

优点

以在不修改任何源代码的情况下，对已有类进行扩展
可以保证组件的划分
可以根据需要，使用已有的功能进行组合，来实现“新”类
很好的避免了类继承的局限性，因为新的业务需要可能就需要创建新的子类

查看父类元组

class Person(object):
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def say(self):
        print("%s is a good man"%(self.name))

class A(object):
    pass
class Worker(Person, A):
    def __init__(self, name, age, gl):
        super().__init__(name, age)
        self.gl = gl
        
# 是元组类型，里面的每个元素是该类的父类
print(Worker.__bases__)

使用Mixin类动态添加父类

#定义一个Mixin类，一般省略object
class FixMixin():
    def fixPhone(self):
        print("修手机")
    def fixComputer(self):
        print("修电脑")
        
class Person(object):
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def say(self):
        print("%s is a good man"%(self.name))

class Student(Person):
    def __init__(self, name, age, stuId):
        super().__init__(name, age)
        self.stuId = stuId
        
# 给pyClass动态添加父类pyMixinClass，flag为真时可以明确pyMixinClass不在pyClass.__bases__中，否则需要mixin函数自己去判断
def mixin(pyClass, pyMixinClass, flag=0):
    if flag:
        pyClass.__bases__ += (pyMixinClass,)
    if pyMixinClass not in pyClass.__bases__:
        pyClass.__bases__ += (pyMixinClass,)
      
# 将FixMixin类动态设置为Student的父类
mixin(Student, FixMixin, 0)

stu = Student("dily", 18, 1)
stu.say()
stu.fixPhone()

六、多态

概念：一种事物的多种形态

终极目标：人可以喂任何一种动物

定义出两个类(猫、狗)，分别带有name属性与eat方法

cat.py

class Cat(object):
    def __init__(self, name):
        self.name = name
    def eat(self):
        print("%s在吃饭"%(self.name))

dog.py

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Dog</span><span class="hljs-params">(object)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name)</span>:</span>
        self.name = name
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">eat</span><span class="hljs-params">(self)</span>:</span>
        print(<span class="hljs-string">"%s在吃饭"</span>%(self.name))

main.py

<span class="hljs-keyword">from</span> cat <span class="hljs-keyword">import</span> Cat
<span class="hljs-keyword">from</span> dog <span class="hljs-keyword">import</span> Dog

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    cat = Cat(<span class="hljs-string">"lele"</span>, <span class="hljs-number">8</span>)
    dog = Dog(<span class="hljs-string">"huanhuan"</span>, <span class="hljs-number">4</span>)
   
<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">"__main__"</span>:
    main()

再添加100种动物，也都是有name属性与eat方法

定义一个Animal类，带有name属性与eat方法，让猫、狗等动物都继承自Animal类

animal.py

class Animal(object):
    def __init__(self, name):
        self.name = name
    def eat(self):
        print("%s在吃饭"%(self.name))

dog.py

from animal import Animal

class Dog(Animal):
    # def __init__(self, name):
    #     self.name = name
    # def eat(self):
    #     print("%s在吃饭"%(self.name))
    pass

cat.py

<span class="hljs-keyword">from</span> animal <span class="hljs-keyword">import</span> Animal
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Cat</span><span class="hljs-params">(Animal)</span>:</span>
    <span class="hljs-comment"># def __init__(self, name):</span>
    <span class="hljs-comment">#     self.name = name</span>
    <span class="hljs-comment"># def eat(self):</span>
    <span class="hljs-comment">#     print("%s在吃饭"%(self.name))</span>
    <span class="hljs-keyword">pass</span>

main.py

<span class="hljs-keyword">from</span> cat <span class="hljs-keyword">import</span> Cat
<span class="hljs-keyword">from</span> dog <span class="hljs-keyword">import</span> Dog

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    cat = Cat(<span class="hljs-string">"lele"</span>, <span class="hljs-number">8</span>)
    dog = Dog(<span class="hljs-string">"huanhuan"</span>, <span class="hljs-number">4</span>)
   
<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">"__main__"</span>:
    main()

定义一个人类，带有feedCat与feedDog方法可以喂猫狗

person.py

class Person(object):
    def feedCat(self, cat):
        cat.eat()
    def feedDog(self, dog):
        dog.eat()

main.py

<span class="hljs-keyword">from</span> person <span class="hljs-keyword">import</span> Person
<span class="hljs-keyword">from</span> cat <span class="hljs-keyword">import</span> Cat
<span class="hljs-keyword">from</span> dog <span class="hljs-keyword">import</span> Dog

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    per = Person()

    cat = Cat(<span class="hljs-string">"lele"</span>, <span class="hljs-number">8</span>)
    dog = Dog(<span class="hljs-string">"huanhuan"</span>, <span class="hljs-number">4</span>)

    per.feedCat(cat)
    per.feedDog(dog)

<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">"__main__"</span>:
    main()

人要喂100种动物，难道要写100个feedXXX吗？

person.py

class Person(object):
    # def feedCat(self, cat):
    #     cat.eat()
    # def feedDog(self, dog):
    #     dog.eat()

    def feedAnimal(self, ani):
        ani.eat()

main.py

<span class="hljs-keyword">from</span> person <span class="hljs-keyword">import</span> Person
<span class="hljs-keyword">from</span> cat <span class="hljs-keyword">import</span> Cat
<span class="hljs-keyword">from</span> dog <span class="hljs-keyword">import</span> Dog

<span class="hljs-comment">#多态：一种事物的多种形态</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    per = Person()

    cat = Cat(<span class="hljs-string">"lele"</span>, <span class="hljs-number">8</span>)
    dog = Dog(<span class="hljs-string">"huanhuan"</span>, <span class="hljs-number">4</span>)

    <span class="hljs-comment"># per.feedCat(cat)</span>
    <span class="hljs-comment"># per.feedDog(dog)</span>
    <span class="hljs-comment"># 人要喂养100种动物</span>
    per.feedAnimal(cat)
    per.feedAnimal(dog)

<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">"__main__"</span>:
    main()

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面向对象编程

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